1. Field of the Invention
This invention relates generally to apparatus and methods for manufacturing optical and photonic devices for fiber optical signal transmission systems. More particularly, this invention is related to robust multiple-layered thin film membrane for configuring and manufacturing micro-opto-electro-mechanical systems (MOEMS) and micro-electro-mechanical systems (MEMS) devices for use in wide-band optical communication sub-system or system.
2. Description of the Related Art
Next generation wide-band optical communication system requires a significant scale-down and low cost from today""s standards, which are based on the components manufactured by mechanical methods. Recent development in silicon based MOEMS and MEMS devices has provided possible pathway to design photonic devices which meet the scaling and cost requirements for the next generation optical system. However, the freestanding multiple-layered thin-film membrane, which is design to achieve desired optical property, often suffer deformations due to mismatches of mechanical or thermal properties among different layers. The deformations could become more severe during device operation because of imposed forces or temperature variations. These deformations can severely degrade the optical and mechanical performances of MOEMS and MEMS devices. The deformations may also cause some electrical hazards such as electrostatic discharge (ESD) and electrical shorts.
Referring to FIGS. 1A and 1B for the deformations that occur in typical freestanding thin-film membrane. In FIG. 1A, a deformation occurs in a two-layered freestanding membrane. The deformations at the edges are caused by the mismatches of material properties between two layers. Referring to FIG. 1B for the deformation of a movable three-layered thin-film membrane where the three layers are formed with non-symmetrical layer profile. The deformation at the edges is caused by differential mismatches between the material properties of the non-symmetrical layers of the top and bottom layers.
Therefore, a need still exists in the art in the field of the optical signal transmission systems to provide a configuration and method of manufacture to provide MOEMS and MEMS devices such that the limitations encountered by current configuration of freestanding multi-layered thin-film membrane can be overcome.
It is therefore an object of the present invention to provide new and improved configuration and methods for manufacturing MOEMS and MEMS devices without tangible deformations of freestanding multi-layered thin-film membranes. With the new and improved structural configurations, the limitations and difficulties of the prior art can be resolved. The present invention provides a systemic design methodology to eliminating/relieve the deformations of freestanding multi-layered thin-film membranes used in MOEMS and MEMS devices.
Briefly, in a preferred embodiment, this invention discloses a configuration of thin-film membrane. This thin-film membrane is freestanding, movable, and made of multiple layers of different materials such as silicon nitride, polycrystalline silicon or the combination of these two. This thin-film membrane can be actuated by external controlling forces such as electrostatic force. This thin-film membrane consists of odd number of layers, e.g., 1 layer, 3 layers, 5 layers, . . . , etc. Moreover, the layer profile of this membrane is symmetric, e.g., the bottommost layer is made to be identical to the topmost layer, the next bottommost layer is made to be identical to the next topmost layer, so on and so forth.